U.S. patent application number 16/624644 was filed with the patent office on 2020-05-28 for roll of film including multilayer birefringent reflective polarizer having low pass axis variation.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Kristy A. Gillette, Matthew B. Johnson, Carl A. Stover.
Application Number | 20200166684 16/624644 |
Document ID | / |
Family ID | 64741979 |
Filed Date | 2020-05-28 |
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United States Patent
Application |
20200166684 |
Kind Code |
A1 |
Gillette; Kristy A. ; et
al. |
May 28, 2020 |
Roll of Film Including Multilayer Birefringent Reflective Polarizer
Having Low Pass Axis Variation
Abstract
Rolls of film are described. In particular, rolls of film
including multilayer birefringent polarizers having low pass axis
variation are described. The multilayer birefringent polarizers
have low pass axis variation across a full crossweb width of the
roll of film.
Inventors: |
Gillette; Kristy A.; (Spring
Valley, WI) ; Johnson; Matthew B.; (Woodbury, MN)
; Stover; Carl A.; (St. Paul, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
64741979 |
Appl. No.: |
16/624644 |
Filed: |
June 26, 2018 |
PCT Filed: |
June 26, 2018 |
PCT NO: |
PCT/IB2018/054707 |
371 Date: |
December 19, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62524992 |
Jun 26, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/305 20130101;
B32B 27/36 20130101; B32B 7/02 20130101; G02F 1/133528 20130101;
G02B 5/3083 20130101; B32B 27/06 20130101 |
International
Class: |
G02B 5/30 20060101
G02B005/30; B32B 27/06 20060101 B32B027/06; G02F 1/1335 20060101
G02F001/1335 |
Claims
1. A roll of film, comprising: a multilayer birefringent reflective
polarizer having a pass axis that varies along a crossweb
direction; wherein the multilayer birefringent reflective polarizer
includes alternating layers of a birefringent layer and an
isotropic layer; wherein the birefringent layer of the multilayer
birefringent reflective polarizer includes polyethylene naphthalate
or a copolymer including polyethylene naphthalate and polyethylene
terephthalate monomers; wherein the pass axis of the multilayer
birefringent reflective polarizer varies by no more than about 1
degree across a full crossweb width of the roll of film; wherein
the full crossweb width is greater than 27 inches; and wherein the
multilayer birefringent reflective polarizer has a contrast ratio
of at least 200:1 after the roll of film is exposed to 90% relative
humidity at 65.degree. C. for 500 hours.
2. The roll of film of claim 1, wherein the multilayer birefringent
reflective polarizer includes at least two optical packets, each
optical packet having a linear layer profile.
3. The roll of film of claim 2, wherein the at least two optical
packets have thicknesses that overlap by at least 80%.
4. The roll of film of claim 1, wherein some of the birefringent
layers of the multilayer birefringent reflective polarizer include
polarizing dyes.
5. The roll of film of claim 1, wherein each of the birefringent
layers of the multilayer birefringent reflective polarizer include
polarizing dyes.
6. A method of assembling a display, comprising: providing a liquid
crystal panel; providing the roll of film of claim 1; converting
the roll of film into at least one converted film part; placing one
of the at least one converted film part directly adjacent to the
liquid crystal panel such that in the assembled display, in an
optical path from the liquid crystal panel to the one of the at
least one converted film part, there are no absorbing polarizing
elements between the liquid crystal panel and the one of the at
least one converted film part.
7. The method of claim 6, wherein placing one of the at least one
converted film part directly adjacent to the liquid crystal panel
includes laminating the one of the at least one converted film part
to the liquid crystal panel.
8. A method of processing a polymeric web comprising: providing a
polymeric multilayer web including alternating layers of a layer
capable of developing birefringence including polyethylene
naphthalate or a copolymer including polyethylene naphthalate and
polyethylene terephthalate monomers, and an isotropic layer;
heating the polymeric multilayer web beyond the glass transition
temperature of the isotropic layer; tentering the polymeric
multilayer web to form a multilayer reflective polarizer such that
the layer capable of developing birefringence develops
birefringence; and after tentering, controlling the instantaneous
change in machine direction tension of the multilayer reflective
polarizer such that the pass axis of the multilayer reflective
polarizer varies by no more than about 1.5 degrees across a full
crossweb width of the multilayer reflective polarizer; wherein the
multilayer reflective polarizer is environmentally stable such that
the multilayer reflective polarizer has a contrast ratio of at
least 200:1 after the multilayer reflective polarizer is exposed to
90% relative humidity at 65.degree. C. for 500 hours.
9. The method of claim 5, wherein tentering includes tentering on a
linear tenter and controlling the instantaneous change in machine
direction tension of the multilayer reflective polarizer includes
limiting crossweb relaxation after tentering.
10. The method of claim 6, wherein limiting crossweb relaxation
after tentering means the crossweb width is reduced by no more than
1%--not including edge trimming--before quenching.
11. The method of claim 6, wherein limiting crossweb relaxation
after tentering means the crossweb width is reduced by no more than
0.5%--not including edge trimming--before quenching.
12. The method of claim 5, wherein tentering includes tentering on
a parabolic tenter and controlling the instantaneous change in
machine direction tension of the multilayer reflective polarizer
includes providing a gap of at least 3 inches in a machine
direction between an end of rails of the parabolic tenter and a
beginning of rails of an isolated takeaway mechanism.
13. The method of claim 9, wherein the gap is at least 4
inches.
14. The method of claim 9, wherein the gap is at least 5
inches.
15. A method of processing a polymeric web comprising: providing a
polymeric multilayer web including alternating layers of a layer
capable of developing birefringence including polyethylene
naphthalate or a copolymer including polyethylene naphthalate and
polyethylene terephthalate monomers, and an isotropic layer;
heating the polymeric multilayer web beyond the glass transition
temperature of the isotropic layer; forming a multilayer reflective
polarizer by tentering the polymeric multilayer web with a total
transverse direction draw ratio of about 6.5 or greater such that
the layer capable of developing birefringence develops
birefringence; wherein the multilayer reflective polarizer is
environmentally stable such that the multilayer reflective
polarizer has a contrast ratio of at least 200:1 after the
multilayer reflective polarizer is exposed to 90% relative humidity
at 65.degree. C. for 500 hours.
Description
BACKGROUND
[0001] Multilayer birefringent reflective polarizers may be
delivered in roll form. Reflective polarizers preferentially
reflect light of one polarization while substantially transmitting
light of an orthogonal polarization. Reflective polarizers have a
pass axis. The pass axis is parallel to the linear polarization of
light that is substantially transmitted.
SUMMARY
[0002] In one aspect, the present disclosure relates to a roll of
film. The roll of film includes a multilayer birefringent
reflective polarizer having a pass axis that varies along a
crossweb direction. The multilayer birefringent reflective
polarizer includes alternating layers of a birefringent layer and
an isotropic layer. The birefringent layer of the multilayer
birefringent reflective polarizer includes polyethylene naphthalate
or a copolymer including polyethylene naphthalate and polyethylene
terephthalate monomers. The pass axis of the multilayer
birefringent reflective polarizer varies by no more than about 1
degree across a full crossweb width of the roll of film. The full
crossweb width is greater than 27 inches, and the multilayer
birefringent reflective polarizer has a contrast ratio of at least
200:1 after the roll of film is exposed to 90% relative humidity at
65.degree. C. for 500 hours.
[0003] In another aspect, the present disclosure relates to a
method of processing a polymeric web. The method includes providing
a polymeric multilayer web including alternating layers of a layer
capable of developing birefringence including polyethylene
naphthalate or a copolymer including polyethylene naphthalate and
polyethylene terephthalate monmers, and an isotropic layer; heating
the polymeric multilayer web beyond the glass transition
temperature of the isotropic layer; tentering the polymeric
multilayer web to form a multilayer reflective polarizer such that
the layer capable of developing birefringence develops
birefringence; and, after tentering, controlling the instantaneous
change in machine direction tension of the multilayer reflective
polarizer such that the pass axis of the multilayer reflective
polarizer varies by no more than about 1.5 degrees across a full
crossweb width of the multilayer reflective polarizer. The
multilayer reflective polarizer is environmentally stable such that
the multilayer reflective polarizer has a contrast ratio of at
least 200:1 after the multilayer reflective polarizer is exposed to
90% relative humidity at 65.degree. C. for 500 hours.
[0004] In yet another aspect, the present disclosure relates to a
method of processing a polymeric web. The method includes providing
a polymeric multilayer web including alternating layers of a layer
capable of developing birefringence including polyethylene
naphthalate or a copolymer including polyethylene naphthalate and
polyethylene terephthalate monomers, and an isotropic layer;
heating the polymeric multilayer web beyond the glass transition
temperature of the isotropic layer; and forming a multilayer
reflective polarizer by tentering the polymeric multilayer web with
a total transverse direction draw ratio of about 6.5 or greater
such that the layer capable of developing birefringence develops
birefringence. The multilayer reflective polarizer is
environmentally stable such that the multilayer reflective
polarizer has a contrast ratio of at least 200:1 after the
multilayer reflective polarizer is exposed to 90% relative humidity
at 65.degree. C. for 500 hours.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a top plan view of a roll of film.
[0006] FIG. 2 is a front elevation cross-section of a multilayer
birefringent reflective polarizer.
[0007] FIG. 3 is a top plan schematic of a parabolic tenter.
[0008] FIG. 4 is a graph of pass axis variation along the crossweb
direction for the examples and comparative examples.
DETAILED DESCRIPTION
[0009] Multilayer birefringent reflective polarizers are formed by
stretching a polymeric web including at least one layer capable of
developing birefringence and one other layer. In some embodiments,
the other layer is an isotropic layer; i.e., the layer is not
designed to become birefringent under the same stretching
conditions as the layer capable of developing birefringence. In
some embodiments, the isotropic layer is isotropic because it does
not develop birefringence due to its molecular structure. In some
embodiments, the isotropic layer is isotropic because it does not
develop birefringence at the same temperature as the layer capable
of developing birefringence.
[0010] Reflective polarizers are useful in displays; particularly
in liquid crystal displays or other transmissive displays that
utilize a backlight for uniform illumination. Reflective polarizers
are typically laminated to, attached to, or disposed next to
conventional absorbing polarizers, in order to provide a sufficient
contrast ratio (the ratio of the maximum to minimum transmission
while the backlight is on) to be useful or acceptable as a display.
However, the lamination/attachment process or the handling and
converting of separate films adds manufacturing cost and
complexity. Further, due to unevenness in stretch during the
orientation process, conventional reflective polarizers have a
large variation in pass axis direction along a crossweb direction.
For some conventional reflective polarizers, the pass axis can vary
along the full crossweb width by 3 degrees or more. The variation
in pass axis direction makes it difficult to align the axes of the
reflective polarizer and absorbing polarizer, which results in a
worse contrast ratio or lower transmission for the display.
Alternatively, a large quantity of material may need to be
discarded in order to find a film component both properly sized and
having suitable levels of pass axis variation.
[0011] Modification of certain process conditions can enable film
rolls of reflective polarizers as described herein. Stretching
conditions for the polymeric multilayer web in particular may have
a significant effect on pass axis variation. For example,
surprisingly high transverse direction draw ratios enabled the
development of highly birefringent interfaces while still
maintaining good uniformity across the crossweb width. In some
embodiments, the total transverse direction draw ratio (i.e., the
ratio of the final transverse width to the initially casted,
pre-stretching width is very high. In some embodiments, the total
transverse direction draw ratio of at least 6. In some embodiments,
the total transverse direction draw ratio is at least 7. In some
embodiments, the total transverse direction draw ratio is at least
7.5.
[0012] In some embodiments, after tentering the polymeric
multilayer web to form a multilayer reflective polarizer, the
instantaneous change in machine direction tension in the multilayer
reflective polarizer is controlled such that the pass axis varies
minimally across the full crossweb width of the multilayer
reflective polarizer. Effective control of instantaneous machine
direction tension across the multilayer reflective polarizer may
utilize different process modifications dependent on the variety of
tenter used in the orientation process.
[0013] For example, for a conventional linear tenter, typical
processing conditions allow for "toe-in," or a crossweb relaxation
immediately post-stretching and before trimming the edges of the
film, in order to improve shrinkage and other physical
characteristics of the film. Films described herein, however, take
advantage of a limited or minimal toe-in in order to surprisingly
preserve a much more uniform pass axis across the full crossweb
width. In some embodiments, the crossweb width is reduced by no
more than 1%, not including edge trimming. In some embodiments, the
crossweb width is reduced by no more than 0.5%, not including edge
trimming.
[0014] In a parabolic tenter, such as the one described in U.S.
Pat. No. 6,949,212 (Merrill et al.) and shown in FIG. 3,
controlling instantaneous machine direction tension across the
multilayer reflective polarizer means extending the gap (in a
machine direction) more than is conventionally done between the end
of the parabolic tenter rails and the beginning of the rails of the
isolated takeaway mechanism. In FIG. 3, this includes moving the
tracks 140 and 141 farther in the machine direction from rollers
62. In some embodiments, the gap is at least 3 inches. In some
embodiments, the gap is at least 4 inches. In some embodiments, the
gap is at least 5.
[0015] FIG. 1 is a top plan view of a roll of film. Roll 100
includes multilayer birefringent reflective polarizer 110.
[0016] Multilayer birefringent reflective polarizer 110 includes
alternating microlayers of at least two different materials.
Multilayer optical films, i.e., films that provide desirable
transmission and/or reflection properties at least partially by an
arrangement of microlayers of differing refractive index, are
known. It has been known to make such multilayer optical films by
depositing a sequence of inorganic materials in optically thin
layers ("microlayers") on a substrate in a vacuum chamber.
[0017] Multilayer optical films have also been demonstrated by
coextrusion of alternating polymer layers. See, e.g., U.S. Pat. No.
3,610,729 (Rogers), U.S. Pat. No. 4,446,305 (Rogers et al.), U.S.
Pat. No. 4,540,623 (Im et al.), U.S. Pat. No. 5,448,404 (Schrenk et
al.), and U.S. Pat. No. 5,882,774 (Jonza et al.). In these
polymeric multilayer optical films, polymer materials are used
predominantly or exclusively in the makeup of the individual
layers. Such films are compatible with high volume manufacturing
processes and can be made in large sheets and roll goods. In some
embodiments, at least one of the materials used in the alternating
polymer layers is either polyethylene naphthalate or a copolymer
that includes polyethylene terephthalate and polyethylene
naphthalate. In some embodiments, at least one of the materials
used in the layers capable of developing birefringence is
polyethylene naphthalate or a copolymer of polyethylene
naphthalate, polyethylene terephthalate, and any other monomer at a
mol % less than 10%, with mol % based on the diacid monomer being
100%.
[0018] A multilayer optical film includes individual microlayers
having different refractive index characteristics so that some
light is reflected at interfaces between adjacent microlayers. The
microlayers are sufficiently thin so that light reflected at a
plurality of the interfaces undergoes constructive or destructive
interference in order to give the multilayer optical film the
desired reflective or transmissive properties. For multilayer
optical films designed to reflect light at ultraviolet, visible, or
near-infrared wavelengths, each microlayer generally has an optical
thickness (a physical thickness multiplied by refractive index) of
less than about 1 .mu.m. Layers may be arranged generally as
thinnest to thickest. In some embodiments, the arrangement of the
alternating optical layers may vary substantially linearly as a
function of layer count. These layer profiles may be referred to as
linear layer profiles. In some embodiments, the thickness of the
layers may be arranged monotonically. Generally, linear layer
profiles are based on the overall shape of the layer arrangement,
and minor or insignificant deviations from a linear layer profile
would still be considered by a person having ordinary skill in the
art as being a linear layer profile. In some embodiments, this may
be referred to as a substantially linear layer profile. Thicker
layers may be included, such as skin layers at the outer surfaces
of the multilayer optical film, or protective boundary layers
(PBLs) disposed within the multilayer optical films, that separate
coherent groupings (referred to herein as "packets") of
microlayers. In some embodiments, multilayer birefringent
reflective polarizer 110 may include at least two packets. In some
embodiments, the two packets of the multilayer birefringent
reflective polarizer have thicknesses that overlap by at least 80%.
In some cases, the protective boundary layer may be the same
material as at least one of the alternating layers of the
multilayer optical film. In other cases, the protective boundary
layer may be a different material, selected for its physical or
rheological properties. The protective boundary layers may be on
one side or on both sides of an optical packet. In the case of a
single-packet multilayer optical film, the protective boundary
layer may be on one or both external surfaces of the multilayer
optical film.
[0019] Skin layers are sometimes added which occurs after the
feedblock but before the melt exits the film die. The multilayer
melt is then cast through a film die onto a chill roll in the
conventional manner for polyester films, upon which it is quenched.
The cast web is then stretched by at least one of a variety of
possible processes to achieve birefringence in at least one of the
optical layers, producing in many cases either a reflective
polarizer or mirror film, as has been described in, for example,
U.S. Patent Publication No. 2007/047080 A1, U.S. Patent Publication
No. 2011/0102891 A1, and U.S. Pat. No. 7,104,776 (Merrill et al.).
The films, having birefringence, may be referred to as multilayer
birefringent reflective polarizers.
[0020] Multilayer birefringent reflective polarizer 110 may have
any suitable reflection characteristics. For example, multilayer
birefringent reflective polarizer 110 may be a reflective polarizer
preferentially reflecting light of one polarization while
preferentially transmitting light of a second orthogonal
polarization. In some embodiments, the multilayer birefringent
reflective polarizer may include or be attached to a quarter-wave
retarder to effectively form a circular reflective polarizer. The
quarter-wave retarder may, in some embodiments, have a retardance
within 50 nm of 137.5 nm for 550 nm light. In some embodiments, the
quarter-wave retarder may be or include a birefringent stretched
polymer film. In some embodiments, the quarter-wave retarder may be
or include a liquid crystal layer. In some embodiments, the
quarter-wave retarder may be achromatic over an extended wavelength
range; that is, the quarter-wave retarder may provide approximately
quarter-wave retardation over that extended wavelength range. In
some embodiments, multilayer birefringent reflective polarizer 110
transmits at least 60% of pass state light from 425 nm to 675 nm at
normal incidence. In some embodiments, multilayer birefringent
reflective polarizer 110 transmits at least 70% of pass state light
from 425 nm to 675 nm at normal incidence.
[0021] In some embodiments, the multilayer birefringent reflective
polarizer includes absorbing elements. In some embodiments, these
absorbing elements are absorbing polarizing elements. In some
embodiments, these absorbing elements are broadband absorbers,
which absorb both orthogonal polarizations of light. In some
embodiments, the absorbing polarizing elements may be disposed only
within the birefringent layers of the multilayer birefringent
reflective polarizer. In some embodiments, the absorbing polarizing
elements may be disposed only within some of the birefringent
layers of the multilayer birefringent reflective polarizer.
Exemplary polarizers including absorbing elements are described in
U.S. Patent Publication No. 2016-0306086 (Haag et al.) and U.S.
Pat. No. 6,096,375 (Ouderkirk et al.).
[0022] The crossweb width of the roll of film is shown in FIG. 1.
Across the full crossweb width of the roll of film, the pass axis
direction may vary by no more than 1.5 degrees, by no more than 1
degree, by no more than 0.8 degrees, or my no more than 0.5
degrees.
[0023] In some embodiments, the full crossweb width of the roll of
film is large. In some embodiments, the full crossweb width of the
roll of film is greater than 27 inches. In some embodiments, it is
greater than 30 inches. In some embodiments, it is greater than 32
inches.
[0024] In some embodiments, the multilayer birefringent reflective
polarizer has highly developed birefringence. In some embodiments,
the difference in index of refraction between two adjacent layers
in-plane, along a block direction (orthogonal to the pass axis) may
be 0.2 or greater. In some embodiments, the different in index of
refraction between two adjacent layers in-plane, along a pass
direction may be 0.05 or less.
[0025] The multilayer birefringent reflective polarizer may have
excellent environmental stability or maintains its performance
after extended exposure to hot or humid conditions. In some
embodiments, multilayer birefringent reflective polarizer has a
contrast ratio of at least 100:1 after the roll of film is exposed
to 90% relative humidity at 65.degree. C. for 500 hours.
[0026] FIG. 2 is a front elevation cross-section of a multilayer
birefringent reflective polarizer. Multilayer birefringent
reflective polarizer includes alternating layer capable of
developing birefringence 212 and isotropic layer 214, and skin
layers 220
[0027] Skin layers 220 may be any suitable thickness and may be
formed from any suitable material. Skin layers 220 may be formed
from or include the same materials as one or more of either the
layer capable of developing birefringence 212 or isotropic layer
214. Skin layers 220 may be thin; in some embodiments, skin layers
may be thinner than 500 nm, thinner than 300 nm, or thinner than
200 nm. In some embodiments, the skin layers should be thicker than
150 nm.
[0028] In some embodiments, rolls of film described herein
including multilayer birefringent reflective polarizers may be
useable in displays or backlights as standalone reflective
polarizers. By standalone reflective polarizers, it is meant that
the reflective polarizers are suitable for use in displays without
lamination to a separate absorbing polarizer. In some embodiments,
the roll of film is converted into at least one converted film
part, and the converted film part is placed directly adjacent to
the liquid crystal panel such that in the assembled display, in an
optical path from the liquid crystal panel to the converted film
part, there are no absorbing polarizing elements between the liquid
crystal panel and the converted film part. In some embodiments,
some of the birefringent layers of the multilayer birefringent
reflective polarizer of the roll of the film may include polarizing
dyes.
Examples
[0029] Multilayer films are typically formed in roll-to-roll
processes wherein the cross-web dimension is commonly labelled
transverse direction (TD) and the dimension along the length of the
roll is called machine direction (MD). Furthermore, the films are
carefully stretched in the forming process in machine direction and
transverse direction in carefully controlled temperature zones to
affect the birefringent layers in what is commonly referred to as a
tentering process. Furthermore, said tentering processes that may
provide either linear transverse stretch or parabolic stretch of
the packets as they are formed; allowance for controlled shrinkage
during the cool down zone may also require a controlled inward
linear retraction commonly referred to as "toe-in". Patent
references describing common multilayer optical film processes are
interspersed in the following examples as are the process
deviations which enable the improved pass axis control for wide
web/film products.
[0030] The examples that follow depict improvements to the pass
axis control across large span web handling equipment. These
improvements come from non-conventional process condition
modifications. The primary metric for improvements to pass axis
control is reported for each example (and comparative example) as a
range of pass axis angle as measured from 25 locations across the
web in the transverse direction.
[0031] Pass Axis Control Definition/Test Method
[0032] Pass axis orientation for 25 locations equidistant across
the useful web width were collected using a rotary analyzer having
ability to report angle to 0.01 degree resolution. Of course, an
idealized case would have no variation in pass axis orientation
between these 25 data points. We define Pass Axis Control as the
peak-to-peak spread in range of measured pass axis orientations
reported in degrees.
Absorbing Material within Multilayer Optical Film Examples
[0033] These examples incorporate a polarizing dye together with
multilayer film packet(s). In the comparative examples (CE-1, CE-2,
CE-3) the dye is incorporated in a layer between two reflective
polarizers as described in U.S. Pat. No. 7,826,009. In Examples
1-3, the dye is in the birefringent layers of one of the reflective
packets as described in U.S. Pre-Grant Patent Publication No.
2016-0306086. Process conditions and pass axis control results are
shown in Tables 1 and 2.
[0034] For Comparative Examples 1, 2, and 3 the dye layer was
in-between the optical packets and is referred to as the "dye
layer". For Examples 1, 2, and 3, the absorbing dye is in the
birefringent layer of one of the packets referred to as the "dye
packet". For these examples PEN is polyethylene naphthalate, PETg
is a co-polyester supplied by Eastman Chemicals (Knoxville, Tenn.),
while PETg-i5 is a polyester based ionomer and is described in U.S.
Pre-Grant Patent Publication 2007-0298271 as "poly-ester O". As
noted, the weight fraction of Petg-i5 used as the isotropic layer
in all these examples is 2 weight % with the remaining 98 weight %
being PETg.
[0035] The tenter heat zones for multilayer optical film line are
controlled for sequential positions, down web, of the
extruder/tenter apparatus. These zones are listed as Pre-heat Temp,
Stretch Temp, Heat Set Temp and Cooling Temp with process settings
tabled along with. We discovered that for hotter heat-set
temperatures (300 F versus 285 F) and reduced toe-in in the
heat-set zone of the tenter (0.3% versus 2.4% width reduction) the
contrast ratio of the reflective polarizer was maintained and the
pass axis range was markedly improved. The rate of change of
tension in the machine direction while the film is maintained at a
temperature near the stretch temperature and subsequently cooled is
believed to be a key parameter when optimizing pass axis range.
[0036] The data in table 1 show comparison for the pass axis
control (i.e. total range of measured pass axis across the web) for
comparative examples (CE-1, CE-2, CE-3) to fall in the 2.13 to 2.79
degree range while the pass axis control for Examples 1-3 falls in
the range of 0.85-1.29 degrees. Also shown in Table 1 are the
measured values for polarization contrast ratio defined as the
average pass state transmission at normal incidence (400-700 nm)
divided by the average block state transmission at normal incidence
(400-700 nm).
[0037] We have demonstrated even further improvements in pass axis
control may be obtained by stretching material twice as wide as
required and winding the roll from the center of the tenter output
while the edges are wound for products with wider pass axis
specifications (examples 2 and 3 are center section rolls from
available film with twice the width).
TABLE-US-00001 TABLE 1 Properties and process conditions for
absorbing material within multilayer optical film Pass Axis
block-state pass-state Number of Number Pre-heat Stretch Heat set
Cooling Range Transmission Transmission Contrast Thickness
micro-layers of optical Temp Temp temp temp (deg) (400-700 nm)
(400-700 nm) Ratio (mils) per packet packets (F.) (F.) (F.) (F.)
Comp Exp 1 2.13 0.030 55.3 1843 2.85 275 2 300 290 285 120 Comp Exp
2 2.79 0.030 54.7 1823 2.96 275 2 300 290 285 120 Comp Exp 3 2.13
0.030 53.7 1790 3.14 275 2 300 290 285 120 Exp 1 1.29 0.012 51.5
4292 2.37 275 2 304 288 300 120 Exp 2 0.85 0.060 52.9 882 2.58 275
2 300 285 300 120 Exp 3 0.96 0.026 52.6 2023 2.56 275 2 300 285 300
120
TABLE-US-00002 TABLE 2 Process conditions for absorbing material
within multilayer optical film Dye Layer % Toe-in Birefringent
Isotropic Rate (pph) in heat- Transverse Line polymer rate polymer
rate Dye Layer (between set and direction Speed Birefringent
(pounds Isotropic (pounds Between optical cooling stretch (fpm)
polymer per hour) polymer per hour) Packets packets) zones ratio
Comp Exp 1 83.8 PEN 335 PETg + PETg- 435 PEN + Dye 167 2.4% 5.7 i5
98/2 Comp Exp 2 83.8 PEN 334 PETg + PETg- 432 PEN + Dye 166 2.4%
5.7 i5 98/2 Comp Exp 3 83.9 PEN 319 PETg + PETg- 430 PEN + Dye 154
2.4% 5.7 i5 98/2 non-dye packet dye packet % Toe-in Birefringent
Birefringent in heat- Transverse Line Birefringent polymer rate
Birefringent layer material set and direction Speed layer (pounds
Isotropic micro-layers layer rate (pounds cooling stretch Exp (fpm)
material per hour) In both packets material per hour) zones ratio
Exp 1 73.2 PEN 243 PETg + PETg- 586 PEN + Dye 216 0.3% 6.20 i5 98/2
Exp 2 67.6 PEN 234 PETg + PETg- 529 PEN + Dye 175 0.3% 6.2 i5 98/2
Exp 3 67.6 PEN 230 PETg + PETg- 521 PEN + Dye 183 0.3% 6.2 i5
98/2
Reflective Polarizer Using True Uniaxial Stretch (Parabolic
Tenter)
[0038] Multilayer reflective polarizers with no absorbing dyes were
produced utilizing a true uniaxial stretch using a parabolic tenter
that is described in U.S. Pat. No. 6,939,499. The process
parameters are described along with the resulting measurements of
pass axis control in Tables 3 and 4.
[0039] For these examples, the number of optical layers was 610,
equally divided between two optical packets (305 microlayers per
packet). The data describing process conditions for these examples
is found in Table 3a and 3b. The distance between the takeaway
belts and the parabolic rails is referred to as the "collision
parameter" and is tabulated in Table 3b.
[0040] The parabolic tenter is divided into five heat zones in the
machine direction with the final zone, zone 5, being the cooling
zone after the stretching is complete. The take away ratio is
defined as the ratio of the speed of the film exiting the
stretching process to the speed of the film entering the stretching
process. This is synonymous with the draw ratio in the machine
direction. For a take away ratio of 0.5 the film has been deformed
so that it is half the length in the machine direction after being
oriented.
[0041] PC/CoPET refers to a polycarbonate/co-polyester blend, which
in this case is Xylex EXXX0281 available from Sabic USA (Houston,
Tex.). PETg is a copolyester available from Eastman Chemicals
(Knoxville, Tenn.). 90/10 CoPEN is a random copolyester that is 90
mol % polyethylene naphthalate and 10 mol % polyethylene
terephthalate produced by 3M Company (Saint Paul, Minn.).
[0042] We have discovered that improved cross pass axis uniformity
is achieved with the higher collision parameters. Pass axis control
for examples 4-6 falls within the range of 0.8 to 0.9 degrees
whereas pass axis control for comparative examples (CE-4, CE-5 and
CE-6) range within 1.6 to 2.7 degrees.
[0043] FIG. 4 shows the pass axis data measured every 2.2 inches in
the transverse (crossweb) direction for examples 4, 5, 6, CE-4,
CE-5, and CE-6. In each case, the contrast ratio of these films was
greater than 3000 due to the large number of layers; large
refractive index difference afforded by the orientation
characteristics of the parabolic tenter; and the carefully
controlled layer thickness profiles for each packet. For Example 6,
the contrast ratio was measured to be 4502.
TABLE-US-00003 TABLE 3 True uniaxial oriented reflective polarizer
process data Birefrigent Layers Isotropic Layers Packet 1 Packet 2
Both packets 90/10 90/10 PC/CoPET PETg CoPEN PEN CoPEN PEN Example
Polymer rate rate Polymer (lb/hr) (lb/hr) Polymer (lb/hr) (lb/hr)
Comparative Xylex/PETg 275 69 90/10 CoPEN 110 40 90/10 CoPEN 111.5
40 Example 4 & PEN & PEN Comparative Xylex/PETg 275 69
90/10 CoPEN 110 40 90/10 CoPEN 111.5 40 Example 5 & PEN &
PEN Comparative Xylex/PETg 275 69 90/10 CoPEN 110 40 90/10 CoPEN
111.5 40 Example 6 & PEN & PEN Example 4 Xylex/PETg 275 69
90/10 CoPEN 110 40 90/10 CoPEN 111.5 40 & PEN & PEN Example
5 Xylex/PETg 275 69 90/10 CoPEN 110 40 90/10 CoPEN 111.5 40 &
PEN & PEN Example 6 Xylex/PETg 275 69 90/10 CoPEN 110 40 90/10
CoPEN 111.5 40 & PEN & PEN
TABLE-US-00004 TABLE 4 True uniaxial oriented reflective polarizer
process data Tenter Tenter Zone Temps (F.) Zone 1 to Transvere Cast
Wheel Inlet Web Zone 4 Z5 Direction Collision Optical Axis Speed
Width (pre-heat (cooling Take Away Stretch Parameter range (deg)
Thickness Example (ft/min) (in) and stretch) zone) Ratio Ratio (in)
over 28.2'' (mils) Comparative 105 18 290 175 0.50 5.44 0.5 2.7
2.463 Example 4 Comparative 105 18 290 175 0.50 5.65 1 2.2 2.44
Example 5 Comparative 105 18 290 175 0.50 5.83 2 1.6 2.34 Example 6
Example 4 105 18 290 175 0.50 6.05 3 0.9 2.247 Example 5 105 18 290
175 0.50 6.25 4 0.8 2.171 Example 6 105 18 290 175 0.50 6.50 5 0.8
2.108
[0044] The following are exemplary embodiments according to the
present disclosure: [0045] Item 1. A roll of film, comprising:
[0046] a multilayer birefringent reflective polarizer having a pass
axis that varies along a crossweb direction; [0047] wherein the
multilayer birefringent reflective polarizer includes alternating
layers of a birefringent layer and an isotropic layer; [0048]
wherein the birefringent layer of the multilayer birefringent
reflective polarizer includes polyethylene naphthalate or a
copolymer including polyethylene naphthalate and polyethylene
terephthalate monomers; [0049] wherein the pass axis of the
multilayer birefringent reflective polarizer varies by no more than
about 1 degree across a full crossweb width of the roll of film;
[0050] wherein the full crossweb width is greater than 27 inches;
and [0051] wherein the multilayer birefringent reflective polarizer
has a contrast ratio of at least 200:1 after the roll of film is
exposed to 90% relative humidity at 65.degree. C. for 500 hours.
[0052] Item 2. The roll of film of item 1, wherein the multilayer
birefringent reflective polarizer includes at least two optical
packets, each optical packet having a linear layer profile. [0053]
Item 3. The roll of film of item 2, wherein the at least two
optical packets have thicknesses that overlap by at least 80%.
[0054] Item 4. The roll of film of item 1, wherein some of the
birefringent layers of the multilayer birefringent reflective
polarizer include polarizing dyes. [0055] Item 5. The roll of film
of item 1, wherein each of the birefringent layers of the
multilayer birefringent reflective polarizer include polarizing
dyes. [0056] Item 6. A method of assembling a display, comprising:
[0057] providing a liquid crystal panel; [0058] providing the roll
of film of claim 1; [0059] converting the roll of film into at
least one converted film part; [0060] placing one of the at least
one converted film part directly adjacent to the liquid crystal
panel such that in the assembled display, in an optical path from
the liquid crystal panel to the one of the at least one converted
film part, there are no absorbing polarizing elements between the
liquid crystal panel and the one of the at least one converted film
part. [0061] Item 7. The method of item 6, wherein placing one of
the at least one converted film part directly adjacent to the
liquid crystal panel includes laminating the one of the at least
one converted film part to the liquid crystal panel. [0062] Item 8.
A method of processing a polymeric web comprising: [0063] providing
a polymeric multilayer web including alternating layers of a layer
capable of developing birefringence including polyethylene
naphthalate or a copolymer including polyethylene naphthalate and
polyethylene terephthalate monomers, and an isotropic layer; [0064]
heating the polymeric multilayer web beyond the glass transition
temperature of the isotropic layer; [0065] tentering the polymeric
multilayer web to form a multilayer reflective polarizer such that
the layer capable of developing birefringence develops
birefringence; and [0066] after tentering, controlling the
instantaneous change in machine direction tension of the multilayer
reflective polarizer such that the pass axis of the multilayer
reflective polarizer varies by no more than about 1.5 degrees
across a full crossweb width of the multilayer reflective
polarizer; [0067] wherein the multilayer reflective polarizer is
environmentally stable such that the multilayer reflective
polarizer has a contrast ratio of at least 200:1 after the
multilayer reflective polarizer is exposed to 90% relative humidity
at 65.degree. C. for 500 hours. [0068] Item 9. The method of item
5, wherein tentering includes tentering on a linear tenter and
controlling the instantaneous change in machine direction tension
of the multilayer reflective polarizer includes limiting crossweb
relaxation after tentering. [0069] Item 10. The method of item 6,
wherein limiting crossweb relaxation after tentering means the
crossweb width is reduced by no more than 1%--not including edge
trimming--before quenching. [0070] Item 11. The method of item 6,
wherein limiting crossweb relaxation after tentering means the
crossweb width is reduced by no more than 0.5%--not including edge
trimming--before quenching. [0071] Item 12. The method of item 5,
wherein tentering includes tentering on a parabolic tenter and
controlling the instantaneous change in machine direction tension
of the multilayer reflective polarizer includes providing a gap of
at least 3 inches in a machine direction between an end of rails of
the parabolic tenter and a beginning of rails of an isolated
takeaway mechanism. [0072] Item 13. The method of item 9, wherein
the gap is at least 4 inches. [0073] Item 14. The method of item 9,
wherein the gap is at least 5 inches. [0074] Item 15. A method of
processing a polymeric web comprising: [0075] providing a polymeric
multilayer web including alternating layers of a layer capable of
developing birefringence including polyethylene naphthalate or a
copolymer including polyethylene naphthalate and polyethylene
terephthalate monomers, and an isotropic layer; [0076] heating the
polymeric multilayer web beyond the glass transition temperature of
the isotropic layer; [0077] forming a multilayer reflective
polarizer by tentering the polymeric multilayer web with a total
transverse direction draw ratio of about 6.5 or greater such that
the layer capable of developing birefringence develops
birefringence; wherein the multilayer reflective polarizer is
environmentally stable such that the multilayer reflective
polarizer has a contrast ratio of at least 200:1 after the
multilayer reflective polarizer is exposed to 90% relative humidity
at 65.degree. C. for 500 hours.
* * * * *